Transcript ch12/atm/ATMFrame.java (cont.)

Chapter 12 – Object-Oriented Design
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Chapter Goals
• To learn about the software life cycle
• To learn how to discover new classes and methods
• To understand the use of CRC cards for class discovery
• To be able to identify inheritance, aggregation, and dependency
relationships between classes
• To master the use of UML class diagrams to describe class
relationships
• To learn how to use object-oriented design to build complex
programs
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
The Software Life Cycle
• Encompasses all activities from initial analysis until
obsolescence
• Formal process for software development
• Describes phases of the development process
• Gives guidelines for how to carry out the phases
• Development process
• Analysis
• Design
• Implementation
• Testing
• Deployment
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Analysis
• Decide what the project is supposed to do
• Do not think about how the program will accomplish tasks
• Output: Requirements document
• Describes what program will do once completed
• User manual: Tells how user will operate program
• Performance criteria
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Design
• Plan how to implement the system
• Discover structures that underlie problem to be solved
• Decide what classes and methods you need
• Output:
• Description of classes and methods
• Diagrams showing the relationships among the classes
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Implementation
• Write and compile the code
• Code implements classes and methods discovered in the design
phase
• Program Run: Completed program
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Testing
• Run tests to verify the program works correctly
• Program Run: A report of the tests and their results
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Deployment
• Users install program
• Users use program for its intended purpose
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
The Waterfall Model
• Sequential process of analysis, design, implementation, testing,
and deployment
• When rigidly applied,
waterfall model did not
work
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
The Spiral Model
• Breaks development process down into multiple phases
• Early phases focus on the construction of prototypes
• Lessons learned from development of one prototype can be
applied to the next iteration
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
The Spiral Model
• Problem: Can lead to many iterations, and process can take too
long to complete
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Activity Levels in the Rational Unified Process
Development process methodology by the inventors of UML
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Extreme Programming
• Strives for simplicity
• Removes formal structure
• Focuses on best practices
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Extreme Programming
• Realistic planning
• Customers make business decisions
• Programmers make technical decisions
• Update plan when it conflicts with reality
• Small releases
• Release a useful system quickly
• Release updates on a very short cycle
• Metaphor
• Programmers have a simple shared story that explains the system
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Extreme Programming
• Simplicity
• Design as simply as possible instead of preparing for future complexities
• Testing
• Programmers and customers write test cases
• Test continuously
• Refactoring
• Restructure the system continuously to improve code and eliminate
duplication
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Extreme Programming
• Pair programming
• Two programmers write code on the same computer
• Collective ownership
• All programmers can change all code as needed
• Continuous integration
• Build the entire system and test it whenever a task is complete
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Extreme Programming
• 40-hour week
• Don’t cover up unrealistic schedules with heroic effort
• On-site customer
• A customer is accessible to the programming team at all times
• Coding standards
• Follow standards that emphasize self-documenting code
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Self Check 12.1
Suppose you sign a contract, promising that you will, for an
agreed-upon price, design, implement, and test a software
package exactly as it has been specified in a requirements
document. What is the primary risk you and your customer are
facing with this business arrangement?
Answer: It is unlikely that the customer did a perfect job with
the requirements document. If you don’t accommodate
changes, your customer may not like the outcome. If you
charge for the changes, your customer may not like the cost.
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Self Check 12.2
Does Extreme Programming follow a waterfall or a spiral model?
Answer: An “extreme” spiral model, with lots of iterations.
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Self Check 12.3
What is the purpose of the “on-site customer” in Extreme
Programming?
Answer: To give frequent feedback as to whether the current
iteration of the product fits customer needs.
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Object-Oriented Design
1. Discover classes
2. Determine responsibilities of each class
3. Describe relationships between the classes
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Discovering Classes
• A class represents some useful concept
• Concrete entities: Bank accounts, ellipses, and products
• Abstract concepts: Streams and windows
• Find classes by looking for nouns in the task description
• Define the behavior for each class
• Find methods by looking for verbs in the task description
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Example: Invoice
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Example: Invoice
• Classes that come to mind: Invoice, LineItem, and
Customer
• Good idea to keep a list of candidate classes
• Brainstorm, simply put all ideas for classes onto the list
• You can cross not useful ones later
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Finding Classes
• Keep the following points in mind:
• Class represents set of objects with the same behavior
o
o
o
Entities with multiple occurrences in problem description are good
candidates for objects
Find out what they have in common
Design classes to capture commonalities
• Represent some entities as objects, others as primitive types
o
Should we make a class Address or use a String?
• Not all classes can be discovered in analysis phase
• Some classes may already exist
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
CRC Card
• Describes a class, its responsibilities, and its collaborators
• Use an index card for each class
• Pick the class that should be responsible for each method (verb)
• Write the responsibility onto the class card
Continued
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
CRC Card
• Indicate what other classes are needed to fulfill responsibility
(collaborators)
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Self Check 12.4
Suppose the invoice is to be saved to a file. Name a likely
collaborator.
Answer: PrintStream
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Self Check 12.5
Looking at the invoice in Figure 4, what is a likely responsibility of
the Customer class?
Answer: To produce the shipping address of the customer.
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Self Check 12.6
What do you do if a CRC card has ten responsibilities?
Answer: Reword the responsibilities so that they are at a
higher level, or come up with more classes to handle the
responsibilities.
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Relationships Between Classes
• Inheritance
• Aggregation
• Dependency
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Inheritance
• Is-a relationship
• Relationship between a more general class (superclass) and a
more specialized class (subclass)
• Every savings account is a bank account
• Every circle is an ellipse (with equal width and height)
• It is sometimes abused
• Should the class Tire be a subclass of a class Circle?
o
The has-a relationship would be more appropriate
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Aggregation
• Has-a relationship
• Objects of one class contain references to objects of another
class
• Use an instance variable
• A tire has a circle as its boundary:
class Tire
{
...
private String rating;
private Circle boundary;
}
• Every car has a tire (in fact, it has four)
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Example
class Car extends Vehicle
{
...
private Tire[] tires;
}
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Dependency
• Uses relationship
• Example: Many of our applications depend on the Scanner
class to read input
• Aggregation is a stronger form of dependency
• Use aggregation to remember another object between method
calls
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
UML Relationship Symbols
Relationship
Symbol
Line Style
Arrow Tip
Inheritance
Solid
Triangle
Interface Implementation
Dotted
Triangle
Aggregation
Solid
Diamond
Dependency
Dotted
Open
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Self Check 12.7
Consider the Bank and BankAccount classes of Chapter 7. How
are they related?
Answer: Through aggregation. The bank manages bank
account objects.
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Self Check 12.8
Consider the BankAccount and SavingsAccount objects of
Chapter 10. How are they related?
Answer: Through inheritance.
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Self Check 12.9
Consider the BankAccountTester class of Chapter 3. Which
classes does it depend on?
Answer: The BankAccount, System, and PrintStream
classes.
Big Java by Cay Horstmann
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley &
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Sons. All rights reserved.
Attributes and Methods in UML Diagrams
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Multiplicities
• any number (zero or more): *
• one or more: 1..*
• zero or one: 0..1
• exactly one: 1
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Aggregation and Association
• Association: More general relationship between classes
• Use early in the design phase
• A class is associated with another if you can navigate from
objects of one class to objects of the other
• Given a Bank object, you can navigate to Customer objects
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Five-Part Development Process
1. Gather requirements
2. Use CRC cards to find classes, responsibilities, and
collaborators
3. Use UML diagrams to record class relationships
4. Use javadoc to document method behavior
5. Implement your program
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Case Study: Printing an Invoice — Requirements
• Task: Print out an invoice
• Invoice: Describes the charges for a set of products in certain
quantities
• Omit complexities
• Dates, taxes, and invoice and customer numbers
• Print invoice
• Billing address, all line items, amount due
• Line item
• Description, unit price, quantity ordered, total price
• For simplicity, do not provide a user interface
• Test program: Adds line items to the invoice and then prints it
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Case Study: Sample Invoice
INVOICE
Sam’s Small Appliances
100 Main Street
Anytown, CA 98765
Description
Toaster
Hair dryer
Car vacuum
Price
29.95
24.95
19.99
Qty
3
1
2
Total
89.85
24.95
39.98
AMOUNT DUE: $154.78
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Case Study: Printing an Invoice — CRC Cards
• Discover classes
• Nouns are possible classes:
Invoice
Address
LineItem
Product
Description
Price
Quantity
Total
Amount Due
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Case Study: Printing an Invoice — CRC Cards
• Analyze classes:
Invoice
Address
LineItem
Product
Description
Price
Quantity
Total
Amount Due
// Records the product and the quantity
//
//
//
//
//
variable of the Product class
variable of the Product class
Not an attribute of a Product
Computed – not stored anywhere
Computed – not stored anywhere
• Classes after a process of elimination:
Invoice
Address
LineItem
Product
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
CRC Cards for Printing Invoice
Invoice and Address must be able to format themselves:
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
CRC Cards for Printing Invoice
Add collaborators to invoice card:
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Copyright © 2009 by John Wiley & Sons. All rights reserved.
CRC Cards for Printing Invoice
Product and LineItem CRC cards:
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
CRC Cards for Printing Invoice
Invoice must be populated with products and quantities:
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Printing an Invoice — UML Diagrams
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Copyright © 2009 by John Wiley & Sons. All rights reserved.
Printing an Invoice — Method Documentation
• Use javadoc documentation to record the behavior of the
classes
• Leave the body of the methods blank
• Run javadoc to obtain formatted version of documentation in
HTML format
• Advantages:
• Share HTML documentation with other team members
• Format is immediately useful: Java source files
• Supply the comments of the key methods
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Method Documentation — Invoice Class
/**
Describes an invoice for a set of purchased products.
*/
public class Invoice
{
/**
Adds a charge for a product to this invoice.
@param aProduct the product that the customer
ordered
@param quantity the quantity of the product
*/
public void add(Product aProduct, int quantity)
{
}
Continued
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Method Documentation — Invoice Class (cont.)
/**
Formats the invoice.
@return the formatted invoice
*/
public String format()
{
}
}
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Method Documentation – LineItem Class
/**
Describes a quantity of an article to purchase and its
price.
*/
public class LineItem
{
/**
Computes the total cost of this line item.
@return the total price
*/
public double getTotalPrice()
{
}
Continued
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Method Documentation — LineItem Class (cont.)
/**
Formats this item.
@return a formatted string of this line item
*/
public String format()
{
}
}
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Method Documentation — Product Class
/**
Describes a product with a description and a price.
*/
public class Product
{
/**
Gets the product description.
@return the description
*/
public String getDescription()
{
}
Continued
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Method Documentation — Product Class (cont.)
/**
Gets the product price.
@return the unit price
*/
public double getPrice()
{
}
}
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Method Documentation — Address Class
/**
Describes a mailing address.
*/
public class Address
{
/**
Formats the address.
@return the address as a string with three lines
*/
public String format()
{
}
}
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
The Class Documentation in the HTML Format
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Printing an Invoice — Implementation
• The UML diagram will give instance variables
• Look for associated classes
• They yield instance variables
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Implementation
• Invoice aggregates Address and LineItem
• Every invoice has one billing address
• An invoice can have many line items:
public class Invoice
{
...
private Address billingAddress;
private ArrayList<LineItem> items;
}
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Implementation
A line item needs to store a Product object and quantity:
public class LineItem
{
...
private int quantity;
private Product theProduct;
}
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Implementation
• The methods themselves are now very easy
• Example:
• getTotalPrice of LineItem gets the unit price of the product
and multiplies it with the quantity:
/**
Computes the total cost of this line item.
@return the total price
*/
public double getTotalPrice()
{
return theProduct.getPrice() * quantity;
}
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
ch12/invoice/InvoicePrinter.java
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/**
This program demonstrates the invoice classes by printing
a sample invoice.
*/
public class InvoicePrinter
{
public static void main(String[] args)
{
Address samsAddress
= new Address("Sam&apos;s Small Appliances",
"100 Main Street", "Anytown", "CA", "98765");
Invoice samsInvoice
samsInvoice.add(new
samsInvoice.add(new
samsInvoice.add(new
= new Invoice(samsAddress);
Product("Toaster", 29.95), 3);
Product("Hair dryer", 24.95), 1);
Product("Car vacuum", 19.99), 2);
System.out.println(samsInvoice.format());
}
}
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
ch12/invoice/Invoice.java
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import java.util.ArrayList;
/**
Describes an invoice for a set of purchased products.
*/
public class Invoice
{
private Address billingAddress;
private ArrayList<LineItem> items;
/**
Constructs an invoice.
@param anAddress the billing address
*/
public Invoice(Address anAddress)
{
items = new ArrayList<LineItem>();
billingAddress = anAddress;
}
Continued
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
ch12/invoice/Invoice.java (cont.)
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/**
Adds a charge for a product to this invoice.
@param aProduct the product that the customer ordered
@param quantity the quantity of the product
*/
public void add(Product aProduct, int quantity)
{
LineItem anItem = new LineItem(aProduct, quantity);
items.add(anItem);
}
Continued
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
ch12/invoice/Invoice.java (cont.)
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/**
Formats the invoice.
@return the formatted invoice
*/
public String format()
{
String r = "
I N V O I C E\n\n"
+ billingAddress.format()
+ String.format("\n\n%-30s%8s%5s%8s\n",
"Description", "Price", "Qty", "Total");
for (LineItem item : items)
{
r = r + item.format() + "\n";
}
r = r + String.format("\nAMOUNT DUE: $%8.2f", getAmountDue());
return r;
}
Continued
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
ch12/invoice/Invoice.java (cont.)
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/**
Computes the total amount due.
@return the amount due
*/
public double getAmountDue()
{
double amountDue = 0;
for (LineItem item : items)
{
amountDue = amountDue + item.getTotalPrice();
}
return amountDue;
}
}
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
ch12/invoice/LineItem.java
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/**
Describes a quantity of an article to purchase.
*/
public class LineItem
{
private int quantity;
private Product theProduct;
/**
Constructs an item from the product and quantity.
@param aProduct the product
@param aQuantity the item quantity
*/
public LineItem(Product aProduct, int aQuantity)
{
theProduct = aProduct;
quantity = aQuantity;
}
Continued
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Copyright © 2009 by John Wiley & Sons. All rights reserved.
ch12/invoice/LineItem.java (cont.)
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/**
Computes the total cost of this line item.
@return the total price
*/
public double getTotalPrice()
{
return theProduct.getPrice() * quantity;
}
/**
Formats this item.
@return a formatted string of this item
*/
public String format()
{
return String.format("%-30s%8.2f%5d%8.2f",
theProduct.getDescription(), theProduct.getPrice(),
quantity, getTotalPrice());
}
}
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Copyright © 2009 by John Wiley & Sons. All rights reserved.
ch12/invoice/Product.java
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/**
Describes a product with a description and a price.
*/
public class Product
{
private String description;
private double price;
/**
Constructs a product from a description and a price.
@param aDescription the product description
@param aPrice the product price
*/
public Product(String aDescription, double aPrice)
{
description = aDescription;
price = aPrice;
}
Continued
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
ch12/invoice/Product.java (cont.)
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/**
Gets the product description.
@return the description
*/
public String getDescription()
{
return description;
}
/**
Gets the product price.
@return the unit price
*/
public double getPrice()
{
return price;
}
}
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
ch12/invoice/Address.java
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/**
Describes a mailing address.
*/
public class Address
{
private String name;
private String street;
private String city;
private String state;
private String zip;
/**
Constructs a mailing address.
@param aName the recipient name
@param aStreet the street
@param aCity the city
@param aState the two-letter state code
@param aZip the ZIP postal code
*/
Continued
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
ch12/invoice/Address.java (cont.)
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public Address(String aName, String aStreet,
String aCity, String aState, String aZip)
{
name = aName;
street = aStreet;
city = aCity;
state = aState;
zip = aZip;
}
/**
Formats the address.
@return the address as a string with three lines
*/
public String format()
{
return name + "\n" + street + "\n"
+ city + ", " + state + " " + zip;
}
}
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Self Check 12.10
Which class is responsible for computing the amount due? What
are its collaborators for this task?
Answer: The Invoice class is responsible for computing the
amount due. It collaborates with the LineItem class.
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Self Check 12.11
Why do the format methods return String objects instead of
directly printing to System.out?
Answer: This design decision reduces coupling. It enables us
to reuse the classes when we want to show the invoice in a
dialog box or on a web page.
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Case Study: An Automatic Teller Machine —
Requirements
• ATM is used by bank customers. A customer has a
• Checking account
• Savings account
• Customer number
• PIN
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Case Study: An Automatic Teller Machine —
Requirements
• Customers can select an account
• The balance of the selected account is displayed
• Then, customer can deposit and withdraw money
• Process is repeated until the customer chooses to exit
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Case Study: An Automatic Teller Machine —
Requirements
• Two separate interfaces:
• GUI that closely mimics an actual ATM
• Text-based interface
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Case Study: An Automatic Teller Machine —
Requirements
• GUI Interface
• Keypad
• Display
• Buttons A, B, C
• Button functions depend on the state of the machine
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Case Study: An Automatic Teller Machine —
Requirements
• At start up the customer is expected to
• Enter customer number
• Press the A button
• The display shows:
Enter Customer Number
A = OK
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Case Study: An Automatic Teller Machine —
Requirements
• The customer is expected to
• Enter a PIN
• Press A button
• The display shows:
Enter PIN
A = OK
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Case Study: An Automatic Teller Machine —
Requirements
• Search for the customer number and PIN
• If it matches a bank customer, proceed
• Else return to start up screen
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Case Study: An Automatic Teller Machine —
Requirements
• If the customer is authorized
• The display shows:
Select Account
A = Checking
B = Savings
C = Exit
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Case Study: An Automatic Teller Machine —
Requirements
• If the user presses C
• The ATM reverts to its original state
• ATM asks next user to enter a customer number
• If the user presses A or B
• The ATM remembers selected account
• The display shows:
Balance = balance of selected account
Enter amount and select transaction
A = Withdraw
B = Deposit
C = Cancel
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Case Study: An Automatic Teller Machine —
Requirements
• If the user presses A or B
• The value entered is withdrawn or deposited
• Simulation: No money is dispensed and no deposit is accepted
• The ATM reverts to previous state
• If the user presses C
• The ATM reverts to previous state
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Case Study: An Automatic Teller Machine —
Requirements
• Text-based interaction
• Read input from System.in instead of the buttons
• Here is a typical dialog:
Enter account number: 1
Enter PIN: 1234
A=Checking, B=Savings, C=Quit: A
Balance=0.0
A=Deposit, B=Withdrawal, C=Cancel: A
Amount: 1000
A=Checking, B=Savings, C=Quit: C
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
An Automatic Teller Machine – CRC Cards
Nouns are possible classes:
ATM
User
Keypad
Display
Display message
Button
State
Bank account
Checking account
Savings account
Customer
Customer number
PIN
Bank
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
CRC Cards for Automatic Teller Machine
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
CRC Cards for Automatic Teller Machine
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
ATM States
1. START: Enter customer ID
2. PIN: Enter PIN
3. ACCOUNT: Select account
4. TRANSACT: Select transaction
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
State Diagram for ATM Class
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
An Automatic Teller Machine – UML Diagrams
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Method Documentation ATM Class
/**
An ATM that accesses a bank.
*/
public class ATM
{
/**
Constructs an ATM for a given bank.
@param aBank the bank to which this ATM connects
*/
public ATM(Bank aBank) { }
/**
Sets the current customer number
and sets state to PIN.
(Precondition: state is START)
@param number the customer number
*/
public void setCustomerNumber(int number) { }
Continued
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Method Documentation ATM Class (cont.)
/**
Finds customer in bank.
If found sets state to ACCOUNT, else to START.
(Precondition: state is PIN)
@param pin the PIN of the current customer
*/
public void selectCustomer(int pin) { }
/**
Sets current account to checking or savings. Sets
state to TRANSACT.
(Precondition: state is ACCOUNT or TRANSACT)
@param account one of CHECKING or SAVINGS
*/
Continued
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Method Documentation ATM Class (cont.)
public void selectAccount(int account) { }
/**
Withdraws amount from current account.
(Precondition: state is TRANSACT)
@param value the amount to withdraw
*/
public void withdraw(double value) { }
...
}
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
An Automatic Teller Machine — Implementation
• Start implementation with classes that don’t depend on others
• Keypad
• BankAccount
• Then implement Customer which depends only on
BankAccount
• This bottom-up approach allows you to test your classes
individually
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
An Automatic Teller Machine — Implementation
• Aggregated classes in UML diagram give instance variables
public class ATM
{
private Bank theBank;
...
}
• From description of ATM states, it is clear that we require
additional instance variables:
public class ATM
{
private int state;
private Customer currentCustomer;
private BankAccount currentAccount;
...
}
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
An Automatic Teller Machine — Implementation
• Most methods are very straightforward to implement
• Consider selectCustomer:
/**
Finds customer in bank.
If found sets state to ACCOUNT, else to START.
(Precondition: state is PIN)
@param pin the PIN of the current customer
*/
Continued
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
An Automatic Teller Machine — Implementation (cont.)
• Description can be almost literally translated to Java
instructions:
public void selectCustomer(int pin)
{
assert state == PIN;
currentCustomer = theBank.findCustomer(customerNumber,
pin);
if (currentCustomer == null)
state = START;
else
state = ACCOUNT;
}
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
ch12/atm/ATM.java
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/**
An ATM that accesses a bank.
*/
public class ATM
{
public static final int CHECKING = 1;
public static final int SAVINGS = 2;
private
private
private
private
private
public
public
public
public
int state;
int customerNumber;
Customer currentCustomer;
BankAccount currentAccount;
Bank theBank;
static
static
static
static
final
final
final
final
int
int
int
int
START = 1;
PIN = 2;
ACCOUNT = 3;
TRANSACT = 4;
Continued
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
ch12/atm/ATM.java (cont.)
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/**
Constructs an ATM for a given bank.
@param aBank the bank to which this ATM connects
*/
public ATM(Bank aBank)
{
theBank = aBank;
reset();
}
/**
Resets the ATM to the initial state.
*/
public void reset()
{
customerNumber = -1;
currentAccount = null;
state = START;
}
Continued
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
ch12/atm/ATM.java (cont.)
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/**
Sets the current customer number
and sets state to PIN.
(Precondition: state is START)
@param number the customer number.
*/
public void setCustomerNumber(int number)
{
assert state == START;
customerNumber = number;
state = PIN;
}
Continued
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
ch12/atm/ATM.java (cont.)
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/**
Finds customer in bank.
If found sets state to ACCOUNT, else to START.
(Precondition: state is PIN)
@param pin the PIN of the current customer
*/
public void selectCustomer(int pin)
{
assert state == PIN;
currentCustomer = theBank.findCustomer(customerNumber, pin);
if (currentCustomer == null)
state = START;
else
state = ACCOUNT;
}
Continued
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
ch12/atm/ATM.java (cont.)
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/**
Sets current account to checking or savings. Sets
state to TRANSACT.
(Precondition: state is ACCOUNT or TRANSACT)
@param account one of CHECKING or SAVINGS
*/
public void selectAccount(int account)
{
assert state == ACCOUNT || state == TRANSACT;
if (account == CHECKING)
currentAccount = currentCustomer.getCheckingAccount();
else
currentAccount = currentCustomer.getSavingsAccount();
state = TRANSACT;
}
Continued
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
ch12/atm/ATM.java (cont.)
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/**
Withdraws amount from current account.
(Precondition: state is TRANSACT)
@param value the amount to withdraw
*/
public void withdraw(double value)
{
assert state == TRANSACT;
currentAccount.withdraw(value);
}
/**
Deposits amount to current account.
(Precondition: state is TRANSACT)
@param value the amount to deposit
*/
public void deposit(double value)
{
assert state == TRANSACT;
currentAccount.deposit(value);
}
Continued
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
ch12/atm/ATM.java (cont.)
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/**
Gets the balance of the current account.
(Precondition: state is TRANSACT)
@return the balance
*/
public double getBalance()
{
assert state == TRANSACT;
return currentAccount.getBalance();
}
/**
Moves back to the previous state.
*/
public void back()
{
if (state == TRANSACT)
state = ACCOUNT;
else if (state == ACCOUNT)
state = PIN;
else if (state == PIN)
state = START;
}
Continued
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
ch12/atm/ATM.java (cont.)
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/**
Gets the current state of this ATM.
@return the current state
*/
public int getState()
{
return state;
}
}
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
ch12/atm/Bank.java
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import
import
import
import
java.io.File;
java.io.IOException;
java.util.ArrayList;
java.util.Scanner;
/**
A bank contains customers with bank accounts.
*/
public class Bank
{
private ArrayList<Customer> customers;
/**
Constructs a bank with no customers.
*/
public Bank()
{
customers = new ArrayList<Customer>();
}
Continued
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
ch12/atm/Bank.java (cont.)
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/**
Reads the customer numbers and pins
and initializes the bank accounts.
@param filename the name of the customer file
*/
public void readCustomers(String filename)
throws IOException
{
Scanner in = new Scanner(new File(filename));
while (in.hasNext())
{
int number = in.nextInt();
int pin = in.nextInt();
Customer c = new Customer(number, pin);
addCustomer(c);
}
in.close();
}
Continued
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
ch12/atm/Bank.java (cont.)
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/**
Adds a customer to the bank.
@param c the customer to add
*/
public void addCustomer(Customer c)
{
customers.add(c);
}
/**
Finds a customer in the bank.
@param aNumber a customer number
@param aPin a personal identification number
@return the matching customer, or null if no customer
matches
*/
public Customer findCustomer(int aNumber, int aPin)
{
for (Customer c : customers)
{
if (c.match(aNumber, aPin))
return c;
}
return null;
}
}
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
ch12/atm/Customer.java
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/**
A bank customer with a checking and a savings account.
*/
public class Customer
{
private int customerNumber;
private int pin;
private BankAccount checkingAccount;
private BankAccount savingsAccount;
/**
Constructs a customer with a given number and PIN.
@param aNumber the customer number
@param aPin the personal identification number
*/
public Customer(int aNumber, int aPin)
{
customerNumber = aNumber;
pin = aPin;
checkingAccount = new BankAccount();
savingsAccount = new BankAccount();
}
Continued
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
ch12/atm/Customer.java (cont.)
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/**
Tests if this customer matches a customer number
and PIN.
@param aNumber a customer number
@param aPin a personal identification number
@return true if the customer number and PIN match
*/
public boolean match(int aNumber, int aPin)
{
return customerNumber == aNumber && pin == aPin;
}
/**
Gets the checking account of this customer.
@return the checking account
*/
public BankAccount getCheckingAccount()
{
return checkingAccount;
}
Continued
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
ch12/atm/Customer.java (cont.)
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/**
Gets the savings account of this customer.
@return the checking account
*/
public BankAccount getSavingsAccount()
{
return savingsAccount;
}
}
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
ch12/atm/ATMSimulator.java
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import java.io.IOException;
import java.util.Scanner;
/**
A text-based simulation of an automatic teller machine.
*/
public class ATMSimulator
{
public static void main(String[] args)
{
ATM theATM;
try
{
Bank theBank = new Bank();
theBank.readCustomers("customers.txt");
theATM = new ATM(theBank);
}
catch(IOException e)
{
System.out.println("Error opening accounts file.");
return;
Continued
}
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
ch12/atm/ATMSimulator.java (cont.)
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Scanner in = new Scanner(System.in);
while (true)
{
int state = theATM.getState();
if (state == ATM.START)
{
System.out.print("Enter customer number: ");
int number = in.nextInt();
theATM.setCustomerNumber(number);
}
else if (state == ATM.PIN)
{
System.out.print("Enter PIN: ");
int pin = in.nextInt();
theATM.selectCustomer(pin);
}
Continued
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
ch12/atm/ATMSimulator.java (cont.)
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else if (state == ATM.ACCOUNT)
{
System.out.print("A=Checking, B=Savings, C=Quit: ");
String command = in.next();
if (command.equalsIgnoreCase("A"))
theATM.selectAccount(ATM.CHECKING);
else if (command.equalsIgnoreCase("B"))
theATM.selectAccount(ATM.SAVINGS);
else if (command.equalsIgnoreCase("C"))
theATM.reset();
else
System.out.println("Illegal input!");
}
else if (state == ATM.TRANSACT)
{
System.out.println("Balance=" + theATM.getBalance());
System.out.print("A=Deposit, B=Withdrawal, C=Cancel: ");
String command = in.next();
Continued
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
ch12/atm/ATMSimulator.java (cont.)
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if (command.equalsIgnoreCase("A"))
{
System.out.print("Amount: ");
double amount = in.nextDouble();
theATM.deposit(amount);
theATM.back();
}
else if (command.equalsIgnoreCase("B"))
{
System.out.print("Amount: ");
double amount = in.nextDouble();
theATM.withdraw(amount);
theATM.back();
}
else if (command.equalsIgnoreCase("C"))
theATM.back();
else
System.out.println("Illegal input!");
}
}
}
}
Continued
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
ch12/atm/ATMSimulator.java (cont.)
Program Run:
Enter account number: 1
Enter PIN: 1234
A=Checking, B=Savings, C=Quit: A
Balance=0.0
A=Deposit, B=Withdrawal, C=Cancel: A
Amount: 1000
A=Checking, B=Savings, C=Quit: C
...
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
ch12/atm/ATMViewer.java
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import java.io.IOException;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
/**
A graphical simulation of an automatic teller machine.
*/
public class ATMViewer
{
public static void main(String[] args)
{
ATM theATM;
try
{
Bank theBank = new Bank();
theBank.readCustomers("customers.txt");
theATM = new ATM(theBank);
}
catch(IOException e)
{
JOptionPane.showMessageDialog(null, "Error opening accounts file.");
return;
}
Continued
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
ch12/atm/ATMViewer.java (cont.)
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JFrame frame = new ATMFrame(theATM);
frame.setTitle("First National Bank of Java");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
}
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
ch12/atm/ATMFrame.java
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import
import
import
import
import
import
import
import
java.awt.FlowLayout;
java.awt.GridLayout;
java.awt.event.ActionEvent;
java.awt.event.ActionListener;
javax.swing.JButton;
javax.swing.JFrame;
javax.swing.JPanel;
javax.swing.JTextArea;
/**
A frame displaying the components of an ATM.
*/
public class ATMFrame extends JFrame
{
private static final int FRAME_WIDTH = 300;
private static final int FRAME_HEIGHT = 300;
private JButton aButton;
private JButton bButton;
private JButton cButton;
private KeyPad pad;
private JTextArea display;
Continued
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
ch12/atm/ATMFrame.java (cont.)
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private ATM theATM;
/**
Constructs the user interface of the ATM frame.
*/
public ATMFrame(ATM anATM)
{
theATM = anATM;
// Construct components
pad = new KeyPad();
display = new JTextArea(4, 20);
aButton = new JButton(" A ");
aButton.addActionListener(new AButtonListener());
bButton = new JButton(" B ");
bButton.addActionListener(new BButtonListener());
Continued
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
ch12/atm/ATMFrame.java (cont.)
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cButton = new JButton(" C ");
cButton.addActionListener(new CButtonListener());
// Add components
JPanel buttonPanel = new JPanel();
buttonPanel.add(aButton);
buttonPanel.add(bButton);
buttonPanel.add(cButton);
setLayout(new FlowLayout());
add(pad);
add(display);
add(buttonPanel);
showState();
setSize(FRAME_WIDTH, FRAME_HEIGHT);
}
Continued
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
ch12/atm/ATMFrame.java (cont.)
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/**
Updates display message.
*/
public void showState()
{
int state = theATM.getState();
pad.clear();
if (state == ATM.START)
display.setText("Enter customer number\nA = OK");
else if (state == ATM.PIN)
display.setText("Enter PIN\nA = OK");
else if (state == ATM.ACCOUNT)
display.setText("Select Account\n"
+ "A = Checking\nB = Savings\nC = Exit");
else if (state == ATM.TRANSACT)
display.setText("Balance = "
+ theATM.getBalance()
+ "\nEnter amount and select transaction\n"
+ "A = Withdraw\nB = Deposit\nC = Cancel");
}
Continued
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
ch12/atm/ATMFrame.java (cont.)
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class AButtonListener implements ActionListener
{
public void actionPerformed(ActionEvent event)
{
int state = theATM.getState();
if (state == ATM.START)
theATM.setCustomerNumber((int) pad.getValue());
else if (state == ATM.PIN)
theATM.selectCustomer((int) pad.getValue());
else if (state == ATM.ACCOUNT)
theATM.selectAccount(ATM.CHECKING);
else if (state == ATM.TRANSACT)
{
theATM.withdraw(pad.getValue());
theATM.back();
}
showState();
}
}
Continued
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
ch12/atm/ATMFrame.java (cont.)
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class BButtonListener implements ActionListener
{
public void actionPerformed(ActionEvent event)
{
int state = theATM.getState();
if (state == ATM.ACCOUNT)
theATM.selectAccount(ATM.SAVINGS);
else if (state == ATM.TRANSACT)
{
theATM.deposit(pad.getValue());
theATM.back();
}
showState();
}
}
Continued
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
ch12/atm/ATMFrame.java (cont.)
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class CButtonListener implements ActionListener
{
public void actionPerformed(ActionEvent event)
{
int state = theATM.getState();
if (state == ATM.ACCOUNT)
theATM.reset();
else if (state == ATM.TRANSACT)
theATM.back();
showState();
}
}
}
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
ch12/atm/KeyPad.java
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import
import
import
import
import
import
import
java.awt.BorderLayout;
java.awt.GridLayout;
java.awt.event.ActionEvent;
java.awt.event.ActionListener;
javax.swing.JButton;
javax.swing.JPanel;
javax.swing.JTextField;
/**
A component that lets the user enter a number, using
a button pad labeled with digits.
*/
public class KeyPad extends JPanel
{
private JPanel buttonPanel;
private JButton clearButton;
private JTextField display;
Continued
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
ch12/atm/KeyPad.java (cont.)
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// Add digit buttons
addButton("7");
addButton("8");
addButton("9");
addButton("4");
addButton("5");
addButton("6");
addButton("1");
addButton("2");
addButton("3");
addButton("0");
addButton(".");
// Add clear entry button
clearButton = new JButton("CE");
buttonPanel.add(clearButton);
Continued
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
ch12/atm/KeyPad.java (cont.)
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class ClearButtonListener implements ActionListener
{
public void actionPerformed(ActionEvent event)
{
display.setText("");
}
}
ActionListener listener = new ClearButtonListener();
clearButton.addActionListener(new
ClearButtonListener());
add(buttonPanel, "Center");
}
Continued
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
ch12/atm/KeyPad.java (cont.)
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/**
Adds a button to the button panel
@param label the button label
*/
private void addButton(final String label)
{
class DigitButtonListener implements ActionListener
{
public void actionPerformed(ActionEvent event)
{
// Don&apos;t add two decimal points
if (label.equals(".")
&& display.getText().indexOf(".") != -1)
return;
// Append label text to button
display.setText(display.getText() + label);
}
}
Continued
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
ch12/atm/KeyPad.java (cont.)
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JButton button = new JButton(label);
buttonPanel.add(button);
ActionListener listener = new DigitButtonListener();
button.addActionListener(listener);
}
/**
Gets the value that the user entered.
@return the value in the text field of the keypad
*/
public double getValue()
{
return Double.parseDouble(display.getText());
}
/**
Clears the display.
*/
public void clear()
{
display.setText("");
}
}
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Self Check 12.12
Why does the Bank class in this example not store an array list of
bank accounts?
Answer: The bank needs to store the list of customers so that
customers can log in. We need to locate all bank accounts of a
customer, and we chose to simply store them in the customer
class. In this program, there is no further need to access bank
accounts.
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.
Self Check 12.13
Suppose the requirements change — you need to save the
current account balances to a file after every transaction and
reload them when the program starts. What is the impact of this
change on the design?
Answer: The Bank class needs to have an additional
responsibility: to load and save the accounts. The bank can
carry out this responsibility because it has access to the
customer objects and, through them, to the bank accounts.
Big Java by Cay Horstmann
Copyright © 2009 by John Wiley & Sons. All rights reserved.